In office equipment, such as digital copiers and facsimile machines, original hard-copy documents are recorded as digital data using what can be generally called a “scanner.” In a typical scanner, a document sheet is illuminated and the light reflected from the document sheet is recorded by a photosensitive device such as a charge coupled device (CCD) array and converted to digital image data. A narrow strip of the document sheet is illuminated as the sheet is moved through a document handler, or the photosensitive device is moved relative to a platen on which the document sheet is placed.
Conventional scanner illuminators include a cold cathode lamp and an opposing mirror; a light emitting diode (LED) bar having multiple LEDs and an opposing mirror; or an LED coupled with a light guide and an opposing mirror. Some of the illumination comes direct from the lamp or LEDs and some is sent across to the mirror and then reflected to the document sheet. Typically about 70% of the illuminating light comes directly from the lamp or LEDs and about 30% of the illuminating light comes from the mirror, with a significant light loss.
Another type of conventional scanner illuminators includes two sets of LEDs. Each set has multiple LEDs. The two sets of LEDs are configured in opposition and combined with a focusing lens. As the illuminating light from the two sets of LEDs is directed at the document sheet, significant light loss can be generated.
In addition to significant light loss, it is a challenge for conventional scanner illuminators to have an even illumination along the narrow strip of the document sheet. Further, the angular distribution of light produced by the conventional scanner illuminators at the document can vary in a fast scan direction. Irregularities in illuminating level and the illuminated area can then occur and result in defects in the final image data.
Thus, there is a need to overcome this and other problems of the prior art and to provide an illuminator having one light source coupled with a plurality of light guides.